This invention relates generally to a resonant gate driver circuit for a power converter that may be used to drive a gas discharge lamp.
Parasitics in power semiconductor devices of switching power converters play a very important role in radio frequency switching applications. Gate circuits of power metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGNTs) and MOS-controlled thyristors (MCTs) have parasitic gate capacitance. The conventional way to drive these devices is through a driver circuit supplying a square wave voltage to the gate circuit. A pulse voltage is applied to turn the gate of the gate circuit on. During turn-on, the parasitic gate capacitance is charged. During turn-off, the charge stored in the parasitic gate capacitance is discharged through the driver circuit. Energy stored in the parasitic gate capacitance of the gate circuit power devices is completely dissipated by the driver circuit. For low switching frequency operation, the energy loss and consequential power consumed due to the parasitic gate capacitance is trivial. However, the energy loss can destroy the IC of the gate driver circuit when operated at a high frequency.
The total gate capacitive loss (i.e. power consumed) can be defined as:
Pg=Ciss Vc2 fs.
For a switching frequency fs=3 MHz, a gate parasitic input capacitance Ciss=2000 pF, and a gate voltage Vc=12 V, the power consumed is 0.86 watts.
This substantial loss will destroy the driver circuit IC.
The invention solves this problem by recovering energy stored in the parasitic capacitance of the gate circuit to improve gate driver efficiency. For radio frequency applications such as electrodeless lamp ballast, and high frequency (e.g., greater than 1 MHz.) and high density power converters, high efficiency gate driver operation becomes crucial for performance of the power system.
According to the invention a resonant gate driver circuit for high frequency power converters uses parasitics of the gate circuit as a part of resonance elements and provides a sinusoidal gate voltage waveform to recycle energy stored in the parasitics of the gate circuit, resulting in a substantial loss reduction in energy losses with high efficiency operation. The advantages of such an inventive gate driver circuit over the conventional approach include an extremely low power dissipation in the gate driver circuit, and lossless switching of a power switching device of the resonant gate circuit.
The main objective of the present invention is to provide a new and efficient gate driver circuit for high frequency power converters, especially for electrodeless lamp ballasts and high power density DC/DC, AC/DC and DC/AC converters operating in and above megahertz switching frequencies.
As mentioned above, with a square wave voltage applied to the gate of the power device in the gate circuit operated at high frequencies, the total charge stored in the parasitic gate input capacitance is completely dissipated by the gate driver circuit itself, which will destroy components of the gate driver circuit. To reduce loss in and improve the efficiency of the gate driver circuit, energy stored in the parasitic input capacitance of the gate circuit is recovered by providing a resonant circuit formed, in part, from the parasitic input capacitance.
In one embodiment, at least one discrete or external (i.e., non-parasitic) resonant inductor is inserted into the gate driver circuit to form a resonant tank with the parasitic input gate capacitance. In that case, during turn off the power switching device, such as MOSFET, energy stored in the input gate capacitance thereof will be transferred to the inductor, and during turn on, the energy stored in the resonant inductor will be transferred again to charge the parasitic input gate capacitance of the power switching device. Thus, energy stored in the parasitic gate input capacitance is recycled every switching period, instead of being dissipated by the gate driver circuit. As a consequence, driver circuit efficiency can be significantly improved.
At least one discrete or external (i.e., non-parasitic) capacitance is preferably also added in the tank circuit to eliminate the effects of variations in the parasitic input capacitance due, e.g., to tolerances from device to device.